Cloning and sequencing of the genes downstream of the wbf gene cluster of Vibrio cholerae serogroup O139 and analysis of the junction genes in other serogroups

The DNA sequence of the O-antigen biosynthesis cluster (wbf) of a recently emergent pathogen, Vibrio cholerae serogroup O139, has been determined. Her e we report the sequence of the genes downstream of the O139 wbfX gene and analysis of the genes flanking the wbf gene cluster in other serogroups. Th e gene downstream of wbfX, designated rjg (right junction gene), is predict ed to be not required for O-antigen biosynthesis but appears to be a hot sp ot for DNA rearrangements. Several variants of the pjg gene (three differen t insertions and a deletion) have been found in other serogroups. DNA dot b lot analysis of 106 V. cholerae strains showed the presence of the left and right junction genes, gmhD and rjg, respectively, in all strains. Further, these genes mapped to a single I-CeuI fragment in all 21 strains analyzed by pulsed-field gel electrophoresis, indicating a close linkage. The insert ion sequence element IS1358, found in both O1 and O139 wb* regions, is pres ent in 61% of the strains tested; interestingly, where present, it is predo minantly linked to the wb* region. These results indicated a cassette-like organization of the wb* region,,vith the conserved genes (gmhD and rjg) fla nking the divergent, serogroup-specific wb* genes and IS1358. A similar org anization of the wb* region in other serogroups raises the possibility of t he emergence of new pathogens by homologous recombination via the junction genes.